Keyboard device

ABSTRACT

A keyboard device includes M driving circuits DC(1)˜DC(M), N transition circuits TC(1)˜TC(N), a control module, M column signal lines C(1)˜C(M), N row signal lines R(1)˜R(N) and M*N key units KU(1,1)˜KU(M,N). The control module performs a scanning process to sequentially scan the M column signal lines C(1)˜C(M) in M scan cycles scan(1)˜scan(M). If the key unit KU(k,x) connected with the k-th column signal line C(k) and the x-th row signal line R(x) is depressed, a scan voltage is transmitted from the k-th column signal line C(k) to the x-th row signal line R(x) through a switch sw(k,x) of the key unit KU(k,x). The transition circuit TC(x) connected with the x-th row signal line R(x) is turned on according to the scan voltage. Consequently, an output voltage Rout(x) from the transition circuit TC(x) has a first voltage level.

CROSS REFERENCE TO RELATED PATENT APPLICATION

This is a continuation of application Ser. No. 15/361,025, filed Nov.24, 2016, which claims priority to U.S. Provisional Patent ApplicationNo. 62/259,689 filed Nov. 25, 2015, and claims the benefit of Taiwanapplication Serial No. 105136441 filed Nov. 9, 2016, the contents ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a keyboard device, and moreparticularly to a keyboard device with an anti-ghosting function.

BACKGROUND OF THE INVENTION

Conventionally, the keys of a keyboard device are arranged in a keyboardmatrix. Since the number of conductor lines used in the keyboard matrixis not very large, the fabricating cost of the keyboard device isreduced and the assembling complexity is simplified. However, theconventional keyboard device usually has a ghosting problem.

FIGS. 1A˜1D schematically illustrate some situations of generating theghosting problem in a keyboard matrix. As shown in the drawings, twocolumn signal lines C(1), C(2) and two row signal lines R(1), R(2) ofthe keyboard matrix extending across each other two define four keyunits KU(1,1), KU(1,2), KU(2,1) and KU(2,2). The key unit KU(1,1) isconnected with the first column signal line C(1) and the first rowsignal line R(1). The key unit KU(1,2) is connected with the firstcolumn signal line C(1) and the second row signal line R(2). The keyunit KU(2,1) is connected with the second column signal line C(2) andthe first row signal line R(1). The key unit KU(2,2) is connected withthe second column signal line C(2) and the second row signal line R(2).In the drawings, the solid dots indicate the depressed key units, andthe open dot indicates the non-depressed key. When one of the key unitsis depressed, the column signal line and the row signal line connectedwith the depressed key unit are electrically conducted. For example, ifthe key unit KU(1,1) is depressed, the first column signal line C(1) andthe first row signal line R(1) are electrically conducted.

A keyboard controller (not shown) will sequentially scan the columnsignal lines and detect the voltage levels of all row signal lines. Incase that the keyboard controller issues a scan signal to the firstcolumn signal line C(1) and the key unit KU(1,1) is depressed, thekeyboard controller determines that the key unit KU(1,1) is depressedaccording to the high level state of the first row signal line R(1).

In the situation of FIG. 1A, the key unit KU(1,1) is not depressed, butthe other key units KU(1,2), KU(2,1) and KU(2,2) are depressed. When thekeyboard controller issues a scan signal to the first column signal lineC(1), the first row signal line R(1) is in the high level state throughthe key units KU(1,2), KU(2,1) and KU(2,2). Under this circumstance, thekeyboard controller erroneously determines that the key unit KU(1,1) isdepressed according to the high level state of the first row signal lineR(1).

In the situation of FIG. 1A, the key unit KU(1,1) is erroneouslydetermined as a depressed key. In the situation of FIG. 1B, the key unitKU(1,2) is erroneously determined as a depressed key. In the situationof FIG. 1C, the key unit KU(2,1) is erroneously determined as adepressed key. In the situation of FIG. 1D, the key unit KU(2,2) iserroneously determined as a depressed key. The erroneously-determinedkeys are called ghost keys.

As mentioned above, the keyboard controller may erroneously determinesthat a specified key unit is depressed when the specified key unit isnot depressed but the neighboring key units are depressed. Under thiscircumstance, the ghosting problem occurs.

Therefore, there is a need of providing a keyboard device with ananti-ghosting function.

SUMMARY OF THE INVENTION

The present invention provides a keyboard device with an anti-ghostingfunction.

An embodiment of the present invention provides a keyboard device. Thekeyboard device includes M driving circuits DC(1)˜DC(M), N transitioncircuits TC(1)˜TC(N), a control module, M column signal lines C(1)˜C(M),and N row signal, wherein M and N are positive integers. The controlmodule includes N input ports and M output ports. The N input ports areelectrically coupled to the N transition circuits TC(1)˜TC(N)respectively, and the M output ports are electrically coupled to the Mdriving circuits DC(1)˜DC(M) respectively. The M column signal linesC(1)˜C(M) are electrically coupled to the M driving circuitsDC(1)˜DC(M), respectively, and the N row signal lines R(1)˜R(N) areelectrically coupled to the N transition circuits TC(1)˜TC(N),respectively. Moreover, M*N intersections are formed by the N row signallines R(1)˜R(N) extending across the M column signal lines C(1)˜C(M);and the M*N key units KU(1,1)˜KU(M,N) are disposed neighboring to theM*N intersections, respectively. A key unit KU(i,j) of the M*N key unitsKU(1,1)˜KU(M,N) includes a switch sw(i,j). A first end of the switchsw(i,j) is connected with a column signal line C(i), and a second end ofthe switch sw(i,j) is connected with a row signal line R(j), wherein iis a positive integer smaller than or equal to M and represents whichcolumn signal line the switch sw(i,j) is connected, and j is a positiveinteger smaller than or equal to N and represents which row signal linethe switch sw(i,j) is connected. When the key unit KU(i,j) is depressed,the column signal line C(i) and the row signal line R(j) areelectrically coupled to each other through the switch sw(i,j). Thecontrol module performs a scanning process to sequentially scan the Mcolumn signal lines C(1)˜C(M) in M scan cycles scan(1)˜scan(M), and thescanning process includes following steps. In a step (a), an initialvalue of k is set, wherein the initial value of k is a positive integersmaller than or equal to M. In a step (b), a scan cycle scan(k) isentered. The step (b) includes steps (b1) and (b2). In the step (b1), ascan voltage is provided to the k-th column signal line C(k) and anun-scan voltage is provided to the column signal lines C(1)˜C(k−1) andC(k+1)˜C(M) through the M output ports, wherein a voltage level of theun-scan voltage is lower than a voltage level of the scan voltage. Inthe step (b2), whether N key units KU(k,1)˜KU(k,N) connected with thek-th column signal line C(k) are conducted through the N transitioncircuits TC(1)˜TC(N) are determined. When a key unit KU(k,x) connectedwith the k-th column signal line C(k) and the x-th row signal line R(x)is depressed, the scan voltage is transmitted from the k-th columnsignal line C(k) to the x-th row signal line R(x) through a switchsw(k,x) of the key unit KU(k,x), and the transition circuit TC(x) isturned on by the scan voltage, so that an output voltage Rout(x) fromthe transition circuit TC(x) has a first voltage level, wherein x is apositive integer smaller than or equal to N. When a key unit KU(m,x)connected with the m-th column signal line C(m) and the x-th row signalline R(x) is depressed, the un-scan voltage is transmitted from the m-thcolumn signal line C(m) to the x-th row signal line R(x) through aswitch sw(m,x) of the key unit KU(m,x), wherein m is a positive integersmaller than or equal to M, and m is not equal to k. If the transitioncircuit TC(x) is turned on, the control module determines that the keyunit KU(k,x) is depressed. If the transition circuit TC(x) is turnedoff, the control module determines that the key unit KU(k,x) is notdepressed. In a step (c), the step (b1) and the step (b2) are repeatedlyperformed according to an updated k corresponding to the un-scannedcolumn signal lines until all of the column signal lines C(1)˜C(M) havebeen scanned once.

Numerous objects, features and advantages of the present invention willbe readily apparent upon a reading of the following detailed descriptionof embodiments of the present invention when taken in conjunction withthe accompanying drawings. However, the drawings employed herein are forthe purpose of descriptions and should not be regarded as limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will becomemore readily apparent to those ordinarily skilled in the art afterreviewing the following detailed description and accompanying drawings,in which:

FIGS. 1A˜1D (prior art) schematically illustrate some situations ofgenerating the ghosting problem in a keyboard matrix;

FIG. 2 is a schematic circuit block diagram illustrating a keyboarddevice with an anti-ghosting function according to an embodiment of thepresent invention;

FIG. 3 is a flowchart illustrating a method for sequentially scanningthe column signal lines of the keyboard device according to anembodiment of the present invention;

FIG. 4 is a schematic detailed circuit diagram illustrating a 4*4keyboard matrix and transition circuits of the keyboard device accordingto the embodiment of the present invention;

FIG. 5 is a schematic circuit diagram illustrating the relationshipbetween a key unit KU(k,x) and the corresponding transition circuitTC(x);

FIG. 6 is a schematic waveform diagram illustrating associated signalsprocessed by the keyboard device as shown in FIG. 4;

FIG. 7 is a schematic circuit diagram illustrating the currents flowingthrough the second row of key units, the fourth row of key units and thecorresponding transition circuits in the scan cycle scan(1);

FIG. 8A is a schematic circuit diagram illustrating an equivalentcircuit of the key units (1,2)˜KU(4,2) and the transition circuit TC(2)in the scan cycle scan(1);

FIG. 8B is a schematic circuit diagram illustrating an equivalentcircuit of the key units (1,4)˜KU(4,4) and the transition circuit TC(4)in the scan cycle scan(1); and

FIG. 9 is a schematic circuit diagram illustrating a keyboard deviceaccording to a second embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Please refer to FIG. 2 and FIG. 4. FIG. 2 is a schematic circuit blockdiagram illustrating a keyboard device with an anti-ghosting functionaccording to an embodiment of the present invention. FIG. 4 is aschematic detailed circuit diagram illustrating a 4*4 keyboard matrixand transition circuits of the keyboard device according to theembodiment of the present invention.

The keyboard device 10 includes a keyboard module 13, a driving module113, a control module 111 and a reading module 115. The keyboard module13 includes a keyboard matrix 131 that is composed of M*N key unitsKU(1,1)˜KU(M,N). These key units KU(1,1)˜KU(M,N) are installed on amembrane circuit board. Since the area of the membrane circuit board islimited, these other main components (for example, the driving module113, the control module 111 and the reading module 115) are installed ona motherboard 11.

As shown in FIG. 2, the driving module 113 includes M driving circuitsDC(1)˜DC(M), and the reading module 115 includes N transition circuitsTC(1)˜TC(N). Two first connectors 117 a and 117 b are also installed onthe motherboard 11. The keyboard module 13 includes two secondconnectors 133 a, 133 b, M column signal lines C(1)˜C(M), N row signallines R(1)˜R(N) and the M*N key units KU(1,1)˜KU(M,N). The firstconnectors 117 a and 117 b can be combined together or separated fromeach other. Similarly, the two second connectors 133 a and 133 b can becombined together or separated from each other. When the keyboard module13 is assembled with the motherboard 11, the first connector 117 a andthe second connector 133 a are connected with each other, and the firstconnector 117 b and the second connector 133 b are connected with eachother. Consequently, the M driving circuits DC(1)˜DC(M) are electricallycoupled to the M column signal lines C(1)˜C(M), and the N transitioncircuits TC(1)˜TC(N) are electrically coupled to the N row signal linesR(1)˜R(N).

Moreover, the control module 11 further includes N input ports 111 b andM output ports 111 a. The M output ports 111 a are electrically coupledto the M driving circuits DC(1)˜DC(M) through M column input linesCin(1)˜Cin(M). The M driving circuits DC(1)˜DC(M) are electricallycoupled to the keyboard matrix 131 through the M column signal linesC(1)˜C(M). The control module 111 is electrically coupled to thetransition circuits TC(1)˜TC(N) of the reading module 115 through N rowread lines. The transition circuits TC(1)˜TC(N) are also electricallycoupled to the keyboard matrix 131 through the N row signal linesR(1)˜R(N). The M column signal lines C(1)˜C(M) and the N row signallines R(1)˜R(N) extend across each other to define the M*N key unitsKU(1,1)˜KU(M,N) of the keyboard matrix 131. The operations of thekeyboard matrix and the transition circuits will be described in FIG. 4.

The control module 111 issues M column output signals to the M drivingcircuits DC(1)˜DC(M) through the M column input lines Cin(1)˜Cin(M). Thedriving circuits DC(1)˜DC(M) selectively issue a scan voltage V_(scan)(for example, 5V) or an un-scan voltage V_(un-scan) (for example, 0V) tothe corresponding key units through the corresponding column signallines C(1)˜C(M). For example, in case that a column output signal in ahigh level state is transmitted from the control module 111 to thedriving circuit DC(1) through the column input line Cin(1), the drivingcircuit DC(1) issues the scan voltage V_(scan) to the key units KU(1,1),KU(1, x), . . . , and KU(1, N) through the column signal line C(1).Whereas, in case that a column output signal in a low level state istransmitted from the control module 111 to the driving circuit DC(1)through the column input line Cin(1), the driving circuit DC(1) issuesthe un-scan voltage V_(un-scan) to the key units KU(1,1), KU(1, x), . .. , and KU(1, N) through the column signal line C(1).

During the k-th scan cycle, the control module 111 scan the key unitsKU(k, 1), KU(k,x), . . . , and KU(k, N) through the k-th column signalline C(k). That is, the control module 111 selects the k-th drivingcircuit DC(k) to issue the scan voltage V_(scan), and allows the otherdriving circuits DC(1)˜DC(k−1) and DC(k+1)˜DC(M) to issue the un-scanvoltage V_(un-scan), wherein k is an integer between 1 and M. After thevoltages of the row signal lines R(1)˜R(N) are received by thetransition circuits TC(1)˜TC(N), the transition circuits TC(1)˜TC(N)generate different output voltages Rout(1)˜Rout(N) to the row read linesaccording to the voltages of the row signal lines R(1)˜R(N). Accordingto the output voltages Rout(1)˜Rout(N) from the transition circuitsTC(1)˜TC(N) of the reading module 115, the control module 111 determineswhether the key units of the keyboard matrix 131 are electricallyconducted.

For example, the control module 111 determines whether the key unitKU(k,x) is electrically conducted or shut off according to the outputvoltage Rout(x). The way of determining whether the key unit KU(k,x) iselectrically conducted or shut off by the transition circuit TC(x) willbe described in FIG. 5.

FIG. 3 is a flowchart illustrating a method for sequentially scanningthe column signal lines of the keyboard device according to anembodiment of the present invention. In accordance with the presentinvention, the control module 111 controls the M driving circuitsDC(1)˜DC(M) to sequentially scan the M column signal lines C(1)˜C(M) inM scan cycles scan(1)˜scan(M).

In a step S41, an initial value of k is set, wherein k is a positiveinteger smaller than or equal to M. For example, the initial value of kis set as 1.

In a step S43, a key units KU(k,1)˜KU(1,N) connected with the k-thcolumn signal line C(k) are scanned in the k-th scan cycle scan(k). Thestep S43 includes two sub-steps S431 and S433.

In the step S431, the control module 111 controls the M driving circuitsDC(1)˜DC(M) through the output ports 111 a. Consequently, the k-thoutput port provides the scan voltage V_(scan) to the k-th column signalline C(k). In addition, the other output ports provide the un-scanvoltage V_(un-scan) to the column signal lines C(1)˜C(k−1) andC(k+1)˜C(M). The voltage level of the un-scan voltage V_(un-scan) islower than the voltage level of the scan voltage V_(scan).

In the step S433, the control module 111 determines whether the keyunits KU(k,1)˜KU(1,N) connected with the k-th column signal line C(k)are conducted or shut off through the N transition circuits TC(1)˜TC(N).For example, the transition circuits TC(1), TC(x) and TC(N) generate theoutput voltages Rout(1), Rout(x) and Rout(N) to the corresponding rowread lines, respectively. According to the voltage levels of the outputvoltages Rout(1), Rout(x) and Rout(N), the control module 111 determineswhether the key units KU(k,1), KU(k,x) and KU (k,N) are depressed (StepsS433 a, S433 b and S433 c). The way of generating the output voltagesRout(1)˜Rout(N) from the transition circuits TC(1)˜TC(N) will bedescribed in FIGS. 4, 5 and 6.

After the scan cycle scan(k) is ended, the step S45 is performed todetermine whether k is smaller than M. If the determining condition ofthe step S45 is satisfied, k is set as k+1 (Step S47) and the steps S431and S433 are repeatedly done according to the updated k. If thedetermining condition of the step S45 is not satisfied, it means thatall of the M column signal lines C(1)˜C(M) have been scanned. Meanwhile,the flowchart is ended.

The way of updating the variable k is not restricted as long as theupdated k is correlated to the un-scanned column signal lines.Similarly, the steps S431 and S433 are repeatedly done according to theupdated k until all of the column signal lines C(1)˜C(M) have beenscanned once.

Please refer to FIG. 4. The key units in different rows have differentsituations. In the first row, all of the key units KU(1,1)˜KU(4, 1) arenot depressed. In the second row, the key unit KU(1,2) is depressed, butthe key units KU(2,2)˜KU(4, 2) are not depressed. In the third row, thekey units KU(1, 3) and KU(2, 3) are depressed, but the key units KU(3,3) and KU(4, 3) are not depressed. In the fourth row, all of the keyunits KU(1,4)˜KU(4,4) are depressed.

In accordance with the present invention, the control module 111determines whether the key units KU(1,1)˜KU(M,N) are depressed orundepressed individually.

FIG. 5 is a schematic circuit diagram illustrating the relationshipbetween a key unit KU(k,x) and the corresponding transition circuitTC(x). The key unit KU(k,x) is one of the plural key units as shown inFIGS. 2 and 4. The key unit KU(k,x) is connected with the column signalline C(k) and the transition circuit TC(x). The control module 111determines whether the key unit KU(k,x) is depressed according to theoutput voltage from the transition circuit TC(x).

As shown in FIG. 5, the key unit KU(k,x) includes a switch sw(k,x) and aresistor r(k,x). A first end of the switch sw(k,x) is connected with thecolumn signal line C(k). A second end of the switch sw(k,x) is connectedwith the row signal line R(x). The column signal line C(k) receives thescan voltage V_(scan) or the un-scan voltage V_(un-scan). When the keyunit KU(k,x) is depressed, the switch sw(k,x) is turned on.Consequently, the column signal line C(k) and the row signal line R(x)are electrically coupled to each other.

The transition circuit TC(x) includes a voltage divider 431, a switchingcircuit 435 and a pull-up circuit 433. A high supply voltage source Vddis connected with a row read node N_(Rout(x)) through the pull-upcircuit 433. The voltage divider 431 is electrically coupled to the rowsignal line R(x). Moreover, the voltage divider 431 generates a voltageat a comparison node N_(b(x)) according to a voltage of the row signalline R(x). The on/off state of the switching circuit 435 is determinedaccording to the voltage at the comparison node N_(b(x)).

An example of the switching circuit 435 includes an NPN-type bipolarjunction transistor BJT(x). The base B(x) of the bipolar junctiontransistor BJT(x) is connected with the row signal line R(x). Theemitter E(x) of the bipolar junction transistor BJT(x) is connected witha ground terminal (Gnd). The collector C(x) of the bipolar junctiontransistor BJT(x) is connected with the high supply voltage source Vddand a k-th input port. When the bipolar junction transistor BJT(x) isturned on, the output voltage Rout(x) in the low voltage state (that is,a first voltage level) is outputted from the transition circuit TC(x).When the bipolar junction transistor BJT(x) is turned off, the outputvoltage Rout(x) in the high voltage state (that is, a second voltagelevel) is outputted from the transition circuit TC(x).

The switching circuit 435 is not restricted to the NPN-type bipolarjunction transistor BJT(x). For example, in another embodiment, theswitching circuit 435 includes a metal-oxide-semiconductor field-effecttransistor (MOSFET), a NOT gate or any other comparable component. It isnoted that the voltage level and the current direction may be variedaccording to the employed components. For example, an inversed voltagelevel may be used for performing the driving action and the readingaction.

FIG. 6 is a schematic waveform diagram illustrating associated signalsprocessed by the keyboard device as shown in FIG. 4. From top to bottom,the voltage signals in the vertical axis are sequentially the voltagesignal of the column signal line C(1), the voltage signal of the columnsignal line C(2), the voltage signal of the column signal line C(3), thevoltage signal of the column signal line C(4), the voltage at thecomparison node N_(b(1)), the output voltage Rout(1), the voltage at thecomparison node N_(b(2)), the output voltage Rout(2), the voltage at thecomparison node N_(b(3)), the output voltage Rout(3), the voltage at thecomparison node N_(b(4)) and the output voltage Rout(4).

The time period between the time point t0 and the time point t1 is afirst time interval T1. The time period between the time point t1 andthe time point t2 is a second time interval T2. The time period betweenthe time point t2 and the time point t3 is a third time interval T3. Thetime period between the time point t3 and the time point t4 is a fourthtime interval T4. The time period between the time point t4 and the timepoint t5 is a fifth time interval T5. Each time period is equal to thetime length of one scan cycle. During the scan cycles scan(1)˜scan(4),the control module 111 controls the driving circuits DC(1)˜DC(4) to scanthe column signal lines C(1)˜C(4). After the scan cyclesscan(1)˜scan(4), the control module 111 performs the above scanningprocess again. That is, the voltage signals in the fifth time intervalT5 is identical to the voltage signals in the first time interval T1.The way of generating the output voltages Rout(1)˜Rout(4) from thetransition circuits TC(1)˜TC(4) in response to the depressed orundepressed state of the key unit will be described as follows.

First of all, the changes of the associated signals in the scan cyclescan(1) are described. In the scan cycle scan(1), the scan voltageV_(scan) (for example, 5V) is provided to the column signal line C(1),and the un-scan voltage V_(un-scan) (for example, 0V) is provided to thecolumn signal lines C(2)˜C(4). The scan voltage V_(scan) is transmittedfrom the column signal line C(1) to the key units KU(1,1)˜KU(1,4). Byreading the output voltages Rout(1)˜Rout(4) from the transition circuitsTC(1)˜TC(4), the control module 111 determines whether the key unitsKU(1,1)˜KU(1,4) are depressed or undepressed.

Since the key unit KU(1,1) is not depressed, the scan voltage V_(scan)from the column signal line C(1) cannot be transmitted to the transitioncircuit TC(1). Under this circumstance, the comparison node N_(b(1)) isin a floating state, and the transistor BJT(1) is turned off. Since thetransistor BJT(1) is turned off, the output voltage Rout(1) is in thehigh level state V_(RoutH). Since the key unit KU(1,2) is depressed, thescan voltage V_(scan) from the column signal line C(1) is transmitted tothe comparison node N_(b(2)) through the switch sw(1,2), the resistorr(1,2) and the voltage divider. Meanwhile, the voltage of the comparisonnode N_(b(2)) is higher than the threshold voltage Vth of the transistorBJT(2), and the transistor BJT(2) is turned on. Since the transistorBJT(2) is turned on, the output voltage Rout(2) is in the low levelstate V_(RoutL). Since the key unit KU(1,3) is depressed, the scanvoltage V_(scan) from the column signal line C(1) is transmitted to thecomparison node N_(b(3)) through the switch sw(1,3), the resistor r(1,3)and the voltage divider. Meanwhile, the voltage of the comparison nodeN_(b(3)) is higher than the threshold voltage Vth of the transistorBJT(3), and the transistor BJT(3) is turned on. Since the transistorBJT(3) is turned on, the output voltage Rout(3) is in the low levelstate V_(RoutL). Since the key unit KU(1,4) is depressed, the scanvoltage V_(scan) from the column signal line C(1) is transmitted to thecomparison node N_(b(4)) through the switch sw(1,4), the resistor r(1,4)and the voltage divider. Meanwhile, the voltage of the comparison nodeN_(b(4)) is higher than the threshold voltage Vth of the transistorBJT(4), and the transistor BJT(4) is turned on. Since the transistorBJT(4) is turned on, the output voltage Rout(4) is in the low levelstate V_(RoutL).

In the first column of key units KU(1,1)˜KU(1,4) of FIG. 4, the key unitKU(1,1) is shut off, but the key units KU(1,2)˜KU(1,4) are conducted.Consequently, the output voltage Rout(1) from the transition circuitTC(1) is in the high level state V_(RoutH), and the output voltagesRout(2)˜Rout(4) from the transition circuit TC(2)˜TC(4) are in the lowlevel state V_(RoutL). According to the voltage levels of the outputvoltages Rout(1)˜Rout(4) in the scan cycle scan(1), the control module111 can determine whether the key units KU(1,1)˜KU(1,4) are depressed orundepressed.

In the scan cycle scan(1), the voltages of the comparison nodesN_(b(2)), N_(b(3)) and N_(b(4)) are all higher than the thresholdvoltage Vth. However, the voltages of the comparison nodes N_(b(2)),N_(b(3)) and N_(b(4)) are somewhat different. For example, the voltageof the comparison node N_(b(2)) is higher than the voltage of thecomparison node N_(b(3)), and the voltage of the comparison nodeN_(b(3)) is higher than the voltage of the comparison node N_(b(4)). Thereason will be described later in FIGS. 7, 8A and 8B.

Then, the changes of the associated signals in the scan cycle scan(2)are described. In the scan cycle scan(2), the scan voltage V_(scan) (forexample, 5V) is provided to the column signal line C(2), and the un-scanvoltage V_(un-scan) (for example, 0V) is provided to the column signallines C(1), C(3) and C(4). The scan voltage V_(scan) is transmitted fromthe column signal line C(2) to the key units KU(2,1)˜KU(2,4). By readingthe output voltages Rout(1)˜Rout(4) from the transition circuitsTC(1)˜TC(4), the control module 111 determines whether the key unitsKU(2,1)˜KU(2,4) are depressed or undepressed.

Since the key unit KU(2,1) is not depressed, the scan voltage V_(scan)from the column signal line C(2) cannot be transmitted to the transitioncircuit TC(1). Under this circumstance, the comparison node N_(b(1)) isin the floating state, and the transistor BJT(1) is turned off. Sincethe transistor BJT(1) is turned off, the output voltage Rout(1) is inthe high level state V_(RoutH). Since the key unit KU(2,2) is notdepressed, the scan voltage V_(scan) from the column signal line C(2)cannot be transmitted to the transition circuit TC(2). Under thiscircumstance, the comparison node N_(b(2)) is in the floating state, andthe transistor BJT(2) is turned off. Since the transistor BJT(2) isturned off, the output voltage Rout(2) is in the high level stateV_(RoutH). Since the key unit KU(2,3) is depressed, the scan voltageV_(scan) from the column signal line C(2) is transmitted to thecomparison node N_(b(3)) through the switch sw(2,3), the resistor r(2,3)and the voltage divider. Meanwhile, the voltage of the comparison nodeN_(b(3)) is higher than the threshold voltage Vth of the transistorBJT(3), and the transistor BJT(3) is turned on. Since the transistorBJT(3) is turned on, the output voltage Rout(3) is in the low levelstate V_(RoutL). Since the key unit KU(2,4) is depressed, the scanvoltage V_(scan) from the column signal line C(2) is transmitted to thecomparison node N_(b(4)) through the switch sw(2,4), the resistor r(2,4)and the voltage divider. Meanwhile, the voltage of the comparison nodeN_(b(4)) is higher than the threshold voltage Vth of the transistorBJT(4), and the transistor BJT(4) is turned on. Since the transistorBJT(4) is turned on, the output voltage Rout(4) is in the low levelstate V_(RoutL).

In the scan cycle scan(3), the scan voltage V_(scan) (for example, 5V)is provided to the column signal line C(3), and the un-scan voltageV-scan (for example, 0V) is provided to the column signal lines C(1),C(2) and C(4). The scan voltage V_(scan) is transmitted from the columnsignal line C(3) to the key units KU(3,1)˜KU(3,4). By reading the outputvoltages Rout(1)˜Rout(4) from the transition circuits TC(1)˜TC(4), thecontrol module 111 determines whether the key units KU(3,1)˜KU(3,4) aredepressed or undepressed. The method of determining whether the keyunits KU(3,1)˜KU(3,4) are depressed or undepressed according to theoutput voltages Rout(1)˜Rout(4) from the transition circuits TC(1)˜TC(4)in the scan cycle scan(3) is similar to the above method, and is notredundantly described herein.

In the scan cycle scan(4), the scan voltage V_(scan) (for example, 5V)is provided to the column signal line C(4), and the un-scan voltageV_(un-scan) (for example, 0V) is provided to the column signal linesC(1), C(2) and C(3). The scan voltage V_(scan) is transmitted from thecolumn signal line C(4) to the key units KU(4,1)˜KU(4,4). By reading theoutput voltages Rout(1)˜Rout(4) from the transition circuitsTC(1)˜TC(4), the control module 111 determines whether the key unitsKU(3,1)˜KU(3,4) are depressed or undepressed. The method of determiningwhether the key units KU(4,1)˜KU(4,4) are depressed or undepressedaccording to the output voltages Rout(1)˜Rout(4) from the transitioncircuits TC(1)˜TC(4) in the scan cycle scan(3) is similar to the abovemethod, and is not redundantly described herein.

The relative locations of the key units KU(1,2), KU(2,2), KU(1,3) andKU(2,3) of FIG. 4 are similar to the relative locations of the key unitsof FIG. 1C. In FIG. 6, the signals associated with the transitioncircuits TC(2) and TC(3) are circumscribed with a dotted frame. Thevoltage levels of the output voltages corresponding to the depressed orundepressed states of the key units KU(1,2), KU(2,2), KU(1,3) andKU(2,3) can be realized according to these signals. In the scan cyclescan(1), the control module 111 determines that the key units KU(1,2)and KU(1,3) are conducted according to the output voltages Rout(2) andRout(3) (that is, in the low level state V_(RoutL)). In the scan cyclescan(2), the control module 111 determines that the key unit KU(2,2) isshut off and KU(2,3) is conducted according to the high level stateV_(RoutH) of the output voltage Rout(2) and the low level stateV_(RoutL) of the output voltage Rout(3).

Please refer to FIG. 4 again. When the scan voltage V_(scan) (forexample, 5V) is provided to the column signal line C(2), the currentsequentially flows from the column signal line C(2) to the column signalline C(1) through the key units KU(2,3) and KU(1,3) because the columnsignal line C(1) is issued with the un-scan voltage (for example, 0V).Because the column signal line C(1) is biased and maintained at theun-scan voltage, the current originated from the scan voltage V_(scan)is incapable of changing voltage level of the column signal line C(1).Consequentially, even if the key unit KU(1,2) is depressed and conductedso that the un-scan voltage is passed to the row signal line R(2), thevoltage of the comparison node N_(b(2)) is not affected. Consequently,the transistor BJT(2) of the transition circuit TC(2) is turned off.Under this circumstance, the control module 111 can accurately determinethat the key unit KU(2,2) is in the undepressed state according to theoff state of the transition circuit TC(2). Consequently, theanti-ghosting purpose can be achieved.

FIG. 7 is a schematic circuit diagram illustrating the currents flowingthrough the second row of key units, the fourth row of key units and thecorresponding transition circuits in the scan cycle scan(1). In theupper side of FIG. 7, the key units KU(1,2)˜KU(4,2) and the transitioncircuit TC(2) are shown. In the lower side of FIG. 7, the key unitsKU(1,4)˜KU(4,4) and the transition circuit TC(4) are shown. Fordescribing the direction of the current, the switches and resistors inthese key units are shown.

In the scan cycle scan(1), the current flows from the high-level columnsignal line C(1) to a row node N_(R(2)) through the switch sw(1,2) andthe resistor r(1,2) of the key unit KU(1,2), and then the current flowsfrom the row node N_(R(2)) to the ground terminal through the resistorrb1(2), the comparison node N_(b(2)) and the resistor rb2(2) of thetransition circuit TC(2). Since the switches sw(2,2), sw(3,2) andsw(4,2) are turned off, the voltage level of the row signal line R(2) isnot affected by the un-scan voltage V_(un-scan) of the column signallines C(2)˜C(4).

In the scan cycle scan(1), the current flows from the high-level columnsignal line C(1) to a row node N_(R(4)) through the switch sw(1,4) andthe resistor r(1,4) of the key unit KU(1,4), and then the current flowsalong four branches. One of the four branches of the current flows fromthe row node N_(R(4)) to the ground terminal through the transitioncircuit TC(4). The other three branches of the current flow to thecolumn signal lines C(2)˜C(4) through the key units KU(2,4)˜KU(4,4).

Since the voltages applied to the column signal lines C(1)˜C(4) aredifferent in different scan cycles, the influences of the depressed keyunits KU(1,4)˜KU(4,4) on the voltage of the row signal line R(4) aredifferent. In the scan cycle scan(1), the scan voltage V_(scan) istransmitted to the row signal line R(4) through the switch sw(1,4)because the key unit KU(1,4) is depressed. Consequently, the voltage ofthe row signal line R(4) is increased. In the scan cycle scan(1), thekey units KU(2,4)˜KU(4,4) are also depressed. However, since the un-scanvoltage V_(un-scan) is transmitted from the column signal linesC(2)˜C(4) to the row signal line R(4) through the switches sw(2,4),sw(3,4) and sw(4,4). Consequently, the voltage of the row signal lineR(4) is decreased.

FIG. 8A is a schematic circuit diagram illustrating an equivalentcircuit of the key unit (1,2) and the transition circuit TC(2) in thescan cycle scan(1). The equivalent circuit 82 of FIG. 8A includes afirst part 821 and a second part 823. The row node N_(R(2)) is connectedbetween the first part 821 and the second part 823. The first part 821includes the resistor r(1,2). The second part 823 includes the resistorsrb1(2) and rb2(2). According to voltage division, the voltage of the rownode N_(R(2)) is given by equation (1):

$\begin{matrix}{V_{{NR}{(2)}} = {\frac{{{rb}\; 1(2)} + {{rb}\; 2(2)}}{{r\left( {1,2} \right)} + {{rb}\; 1(2)} + {{rb}\; 2(2)}} \times V_{scan}}} & {{equation}\mspace{14mu}(1)}\end{matrix}$

Moreover, according to voltage division, the voltage of the comparisonnode N_(b(2)) is given by equation (2):

$\begin{matrix}\begin{matrix}{V_{{Nb}{(2)}} = {V_{{NR}{(2)}} \times \frac{{rb}\; 2(2)}{{{rb}\; 1(2)} + {{rb}\; 2(2)}}}} \\{= {\frac{{rb}\; 2(2)}{{r\left( {1,2} \right)} + {{rb}\; 1(2)} + {{rb}\; 2(2)}} \times V_{scan}}}\end{matrix} & {{equation}\mspace{14mu}(2)}\end{matrix}$

FIG. 8B is a schematic circuit diagram illustrating an equivalentcircuit of the key unit (1,4) and the transition circuit TC(4) in thescan cycle scan(1). The equivalent circuit 84 of FIG. 8B includes afirst part 841 and a second part 843. The row node N_(R(4)) is connectedbetween the first part 841 and the second part 843. The first part 841includes the resistor r(1,4). The second part 843 includes the resistorsr(2,4), r(3,4), r(4,4), rb1(4) and rb2(4). The second part 843 isdivided into two sub-parts 843 a and 843 b. The sub-part 843 a includesthe resistors r(2,4), r(3,4) and r(4,4), which are included in thekeyboard matrix. The sub-part 843 b includes the resistors rb1(4) andrb2(4), which are included in the transition circuit TC(4).

The equivalent resistance rb4 of the serially-connected resistors rb1(4)and rb2(4) is expressed as: rb(4)=rb1(4)+rb2(4). The equivalentresistance r_(//) of the resistors r(2,4), r(3,4), r(4,4) and rb4 inparallel is given by equation (3):

$\begin{matrix}{r_{//} = {{{{{r\left( {2,4} \right)}//{r\left( {3,4} \right)}}//{r\left( {4,4} \right)}}//{{rb}(4)}} = \frac{1}{\frac{1}{r\left( {2,4} \right)} + \frac{1}{r\left( {3,4} \right)} + \frac{1}{r\left( {4,4} \right)} + \frac{1}{{rb}(4)}}}} & {{equation}\mspace{14mu}(3)}\end{matrix}$

According to voltage division, the voltage of the row node N_(R(4)) isobtained according to the relationship between the resistor r(1,4) andthe equivalent resistance r_(//). The voltage of the row node N_(R(4))is given by equation (4):

$\begin{matrix}{V_{{NR}{(4)}} = {\frac{r_{//}}{{r\left( {1,4} \right)} + r_{//}} \times V_{scan}}} & {{equation}\mspace{14mu}(4)}\end{matrix}$

Similarly, according to voltage division, the voltage of the comparisonnode N_(b(4)) is given by equation (5):

$\begin{matrix}{V_{{Nb}{(4)}} = {V_{{NR}{(4)}} \times \frac{{rb}\; 2(4)}{{{rb}\; 1(4)} + {{rb}\; 2(4)}}}} & {{equation}\mspace{14mu}(5)}\end{matrix}$

Please refer to FIGS. 8A and 8B. Generally, rb1(2)=rb1(4), andrb2(2)=rb2(4). The control module 111 determines whether the key unitKU(1,4) is depressed according to the voltage of the comparison nodeN_(b(4)). When the key unit KU(1,4) is depressed, regardless of whetherone, two or three of the key units KU(2,4), KU(3, 4) and KU(4,4) aredepressed, the voltage of the row node NR(4) has to be high enough. Forexample, the voltage of the row node NR(4) is higher than the thresholdvoltage (for example, 0.7V) of the transistor BJT(4). Consequently, thetransition circuit TC(4) can make the accurate determination.

From equation (1) and equation (4), the coefficients to be multiplied bythe scan voltage V_(scan) influence the voltages of the row nodesN_(R(2)) and N_(R(4)). Since the equivalent resistance r_(//) is theresistance of plural resistors, the equivalent resistance r_(//) iscertainly lower than the equivalent resistance rb(2) of the resistorsrb1(2) and rb2(2), wherein rb(2)=rb1(2)+rb2(2). In other words, thevoltage of the row node N_(R(4)) in equation (4) is lower than thevoltage of the row node N_(R(2)) in equation (1), and the voltage of thecomparison node N_(b(4)) in equation (5) is lower than the voltage ofthe comparison node N_(b(2)) in equation (2).

Please refer to FIGS. 8A and 8B again. When more key units in the samerow are depressed, the number of the parallel-connected resistors isincreased. Consequently, the voltage of the comparison node N_(b(x)) isdecreased. As mentioned above in FIG. 6, the voltages of the comparisonnodes N_(b(2)), N_(b(3)) and N_(b(4)) are somewhat different in the scancycle. In the second row, only one key unit KU(1,2) is depressed. In thethird row, two key units KU(1,3) and KU(2,3) are depressed. In thefourth row, four key units KU(1,4)˜KU(4,4) are depressed. Consequently,the voltage V1 on of the comparison node N_(b(2)) is higher than thevoltage V2 on of the comparison node N_(b(3)), and the voltage V2 on ofthe comparison node N_(b(3)) is higher than the voltage V4 on of thecomparison node N_(b(4)).

When more key units in the same row are depressed simultaneously, thevoltage of the comparison voltage may be too low. Under thiscircumstance, the transistor BJT is possibly turned off. If thetransistor BJT is erroneously turned off, the voltage level of the rowread node N_(Rout(x)) is adversely affected. That is, the low levelstate V_(RoutL) of the output voltage Rout(1)˜Rout(N) is erroneouslychanged to the high level state V_(RoutH).

For solving the above drawbacks, the voltages of the comparison nodesN_(b(1))˜N_(b(N)) should be higher than the threshold voltage (forexample, 0.7V) of the transistor BJT. Consequently, the transistor BJTis maintained in the on state when many key units in the same row aredepressed. In practical application, it can be assumed a design scenariothat all key units in a same row, for example, KU(1,x)˜KU(M,x) which areelectrically connected to the x-th column, are depressed simultaneously.In the design scenario, the voltage of the comparison node N_(b(x))needs to be at least equivalent to t the threshold voltage Vth of thetransistor BJT(x), and a threshold value of the scan voltage V_(scan)(V_(scan-th)) can be obtained accordingly. Afterwards, the scan voltageV_(scan) to be issued by the keyboard controller is required to begreater than or equivalent to the threshold value of the scan voltage(V_(scan-th)), that is, V_(scan)≥V_(scan-th). Therefore, it can beassured that voltage level of the base B(x) of the bipolar junctiontransistor BJT(x) is always at least 0.7V greater than voltage level thecollector C(x) of the bipolar junction transistor BJT(x), regardlesswhether more than one key unit in the same row is depressed. Based onsuch design scenario, the BJT(x) will not be accidently turned off whenplural key units in the same row are depressed simultaneously.

In case that the number of columns in the keyboard matrix is increased,the keyboard device of the present invention is additionally equippedwith a boost circuit to provide a higher scan voltage V_(scan) to thedriving circuits. After a boost voltage Vup from the boost circuit isreceived by the driving circuit, the voltage level of the scan voltageV_(scan) is increased. As the voltage level of the scan voltage V_(scan)is increased, the voltage of the comparison node is increased.Consequently, the transistor BJT is maintained in the on state when manykey units in the same row are depressed. For example, if the keyboardmatrix has 8 columns of key units, the scan voltage V_(scan) isincreased to 15V by the boost circuit. Even if the number of theparallel-connected resistors is increased, the voltage level of the scanvoltage V_(scan) increased to by the boost circuit is sufficient toincrease the voltages of the comparison nodes N_(b(1))˜N_(b(N)).Consequently, the transistors BJT(1)˜BJT(N) can be effectively turned onwhen the corresponding key units are depressed.

In case that the keyboard matrix has 144 key units, these key units arearranged in 8*18, 12*12 or 18*8 array. The magnitude of the boostvoltage Vup from the boost circuit is determined according to the columnnumber of the keyboard matrix. The increased column number indicatesthat more key units in the same row are possibly depressedsimultaneously. Since the number of the parallel-connected resistors isincreased, the equivalent resistance is reduced. That is, as the columnnumber is increased, the magnitude of the boost voltage iscorrespondingly increased.

For example, in case that the keyboard matrix are arranged in 8*18array, eight switches and eight resistors in each row are connected witheach other in parallel. In this situation, the boost voltage Vup fromthe boost circuit is 15V. In case that the keyboard matrix are arrangedin 18*8 array, eighteen switches and eighteen resistors in each row areconnected with each other in parallel. In this situation, the boostvoltage Vup from the boost circuit is 24V. That is, the magnitude of theboost voltage can be determined according to the practical requirements.

FIG. 9 is a schematic circuit diagram illustrating a keyboard deviceaccording to a second embodiment of the present invention. The keyboardmatrix 931, the reading module 915 and the driving circuits DC(1)˜DC(M)are similar to those of FIG. 2, and are not redundantly describedherein. The keyboard device of this embodiment further includes a boostcircuit 9130. The boost circuit 9130 is included in the driving module913. The boost circuit 9130 provides a boost voltage Vup with a highervoltage level to the driving circuits DC(1)˜DC(M). Moreover, the controlmodule 911 includes a multiplexer 9115 and/or a demultiplexer 9113.

In case that the control module 911 includes the demultiplexer 9113, acontroller 9111 of the control module 911 includes a controller outputport 9111 a and Q column select ports 9111 b, wherein Q is a positiveinteger smaller than M. The controller 9111 provides a scan voltageV_(scan) through the controller output port 9111 a. In case that thecontrol module 911 includes the multiplexer 9115, the controller 9111includes a controller input port 9111 d and P select ports 9111 c. Thecontroller 9111 receives the output voltages Rout(1)˜Rout(N) through thecontroller input port 9111 d, wherein P is a positive integer smallerthan N.

The demultiplexer 9113 includes a demultiplexer input port 9113 c, Qcolumn set ports 9113 a and M driving output ports 9113 b. Thedemultiplexer input port 9113 c is connected with the controller outputport 9111 a through a controller output line MCUout. The Q column setports 9113 a are electrically coupled to the Q column select ports 9111b through controller column select lines Csel(1)˜Csel(Q), respectively.The M driving output ports 9113 b are electrically coupled to the Mdriving circuits DC(1)˜DC(M), respectively. The use of the demultiplexer9113 can reduce the pin number of the controller 9111. In practice, thenumber of the output pins of the demultiplexer 9113 is larger than orequal to the number of the driving circuits DC(1)˜DC(M). Moreover, thetype of the demultiplexer 9113 is determined according to the columnnumber of the keyboard matrix.

The multiplexer 9115 includes a multiplexer output port 9115 c, P rowset ports 9115 a, and N transition input ports 9115 b. The multiplexeroutput port 9115 c is electrically coupled to the controller input port9111 d through a controller input line MCUin. The P row set ports 9115 aare electrically coupled to the P select ports 9111 c through controllerrow select lines Rsel(1)˜Rsel(P), respectively. The N transition inputports 9115 b are electrically coupled to the N transition circuitsTC(1)˜TC(N), respectively. The use of the multiplexer 9115 can reducethe pin number of the controller 9111. In practice, the number of theinput pins of the multiplexer 9115 is larger than or equal to the numberof the transition circuits TC(1)˜TC(N). Moreover, the type of themultiplexer 9115 is determined according to the row number of thekeyboard matrix.

From the above descriptions, the present invention provides a keyboarddevice. In each scan cycle, the keyboard device can accurately determinewhether the key units in the same column are depressed or undepressed.Consequently, the anti-ghosting purpose is achieved. Since the accuracyof determining the depressed states of the key units is enhanced, thekeyboard device of the present invention is more competitive. Moreover,since the transition circuit uses the BJT transistor, the fabricatingcost is largely reduced when compared with the prior art technology.

While the invention has been described in terms of what is presentlyconsidered to be the most practical and preferred embodiments, it is tobe understood that the invention needs not be limited to the disclosedembodiment. On the contrary, it is intended to cover variousmodifications and similar arrangements included within the spirit andscope of the appended claims which are to be accorded with the broadestinterpretation so as to encompass all such modifications and similarstructures.

What is claimed is:
 1. A keyboard device, comprising: M column signallines C(1)˜C(M); N row signal lines R(1)˜R(N), wherein M and N arepositive integers, wherein M*N intersections are formed by the N rowsignal lines R(1)˜R(N) extending across the M column signal linesC(1)˜C(M); N transition circuits TC(1)˜TC(N), electrically coupled tothe N row signal lines R(1)˜R(N) respectively; a control modulecomprising N input ports and M output ports, wherein the N input portsare electrically coupled to the N transition circuits TC(1)˜TC(N)respectively, and the M output ports are electrically coupled to the Mcolumn signal lines C(1)˜C(M) respectively; and M*N key unitsKU(1,1)˜KU(M,N) disposed neighboring to the M*N intersections,respectively, wherein a key unit KU(i,j) of the M*N key unitsKU(1,1)˜KU(M,N) comprises a switch sw(i,j), wherein a first end of theswitch sw(i,j) is connected with a column signal line C(i), a second endof the switch sw(i,j) is connected with a row signal line R(j), i is apositive integer smaller than or equal to M and represents a columnsignal line which the switch sw(i,j) is connected, and j is a positiveinteger smaller than or equal to N and represents a row signal linewhich the switch sw(i,j) is connected, wherein when the key unit KU(i,j)is depressed, the column signal line C(i) and the row signal line R(j)are electrically coupled to each other through the switch sw(i,j);wherein the control module performs a scanning process to sequentiallyscan the M column signal lines C(1)˜C(M) in M scan cyclesscan(1)˜scan(M), and the scanning process comprises steps of: (a)setting an initial value of k, wherein the initial value of k is apositive integer smaller than or equal to M; (b) entering a scan cyclescan(k); (b1) providing a scan voltage to a k-th column signal line C(k)and providing an un-scan voltage to the column signal lines C(1)˜C(k−1)and C(k+1)˜C(M) through the M output ports, wherein a voltage level ofthe un-scan voltage is lower than a voltage level of the scan voltage;(b2) determining whether N key units KU(k,1)˜KU(k,N) connected with thek-th column signal line C(k) are conducted through the N transitioncircuits TC(1)˜TC(N), wherein when a key unit KU(k,x) connected with thek-th column signal line C(k) and the x-th row signal line R(x) isdepressed, the scan voltage is transmitted from the k-th column signalline C(k) to the x-th row signal line R(x) through a switch sw(k,x) ofthe key unit KU(k,x), and a transition circuit TC(x) being coupled tothe x-th row signal line R(x) outputs a first voltage level, wherein xis a positive integer smaller than or equal to N, wherein when a keyunit KU(m, x) connected with the m-th column signal line C(m) and thex-th row signal line R(x) is depressed, the un-scan voltage istransmitted from the m-th column signal line C(m) to the x-th row signalline R(x) through a switch sw(m, x) of the key unit KU(m, x) so that thetransition circuit TC(x) being coupled to the x-th row signal line R(x)is incapable of outputting the first voltage level, wherein m is apositive integer smaller than or equal to M, and m is not equal to k;wherein if the transition circuit TC(x) outputs the first voltage level,the control module determines that the key unit KU(k,x) is depressed,wherein if the transition circuit TC(x) stops outputting the firstvoltage level, the control module determines that the key unit KU(k,x)is not depressed; and (c) repeatedly performing the step (b1) and thestep (b2) according to an updated k corresponding to the un-scannedcolumn signal lines until all of the column signal lines C(1)˜C(M) havebeen scanned once.
 2. The keyboard device as claimed in claim 1, whereinif k is smaller than M in the step (c), k+1 is set as the updated k. 3.The keyboard device as claimed in claim 1, wherein the transistorcircuit TC(x) comprises an NPN-type bipolar junction transistor BJT(x),wherein a base B(x) of the bipolar junction transistor BJT(x) isconnected with the row signal line R(x), an emitter E(x) of the bipolarjunction transistor BJT(x) is connected with a ground terminal, and acollector C(x) of the bipolar junction transistor BJT(x) is connectedwith a high supply voltage source and a k-th input port, wherein whenthe bipolar junction transistor BJT(x) is turned on in the scan cyclescan(k), the transition circuit TC(x) outputs the first voltage level,wherein when the bipolar junction transistor BJT(x) is turned off in thescan cycle scan(k), the transition circuit TC(x) outputs a secondvoltage level.
 4. The keyboard device as claimed in claim 3, where inthe first voltage level is a low level state and the second voltagelevel is a high level state.
 5. The keyboard device as claimed in claim1, further comprising: M driving circuits DC(1)˜DC(M), electricallycoupled to the M column signal lines C(1)˜C(M), respectively.
 6. Thekeyboard device as claimed in claim 5, wherein the keyboard devicefurther comprises a first connector and a second connector, wherein thefirst connector, the M driving circuits DC(1)˜DC(M), the N transitioncircuits TC(1)˜TC(N) and the control module are installed on amotherboard, wherein the second connector, the M column signal linesC(1)˜C(M), the N row signal lines R(1)˜R(N) and the M*N key unitsKU(1,1)˜KU(M,N) are installed on a keyboard module, wherein when thekeyboard module is assembled with the motherboard, the first connectorand the second connector are connected with each other, the M drivingcircuits DC(1)˜DC(M) are electrically coupled to the M column signallines C(1)˜C(M), and the N transition circuits TC(1)˜TC(N) areelectrically coupled to the N row signal lines R(1)˜R(N).
 7. Thekeyboard device as claimed in claim 5, wherein the control modulecomprises: a controller comprising a controller output port and Q columnselect ports, wherein Q is a positive integer smaller than M; and ademultiplexer comprising a demultiplexer input port, Q column set portsand M driving output ports, wherein the demultiplexer input port isconnected with the controller output port, the Q column set ports areelectrically coupled to the Q column select ports, and the M drivingoutput ports are electrically coupled to the M driving circuits.
 8. Thekeyboard device as claimed in claim 5, wherein the keyboard devicefurther comprises a boost circuit electrically coupled to the M drivingcircuits DC(1)˜DC(M), wherein the boost circuit provides a boost voltageto increase the scan voltage.
 9. The keyboard device as claimed in claim8, wherein magnitude of the boost voltage increases when M becomesgreater.
 10. The keyboard device as claimed in claim 1, wherein thecontrol module comprises: a controller comprising a controller inputport and P select ports, wherein P is a positive integer smaller than N;and a multiplexer comprising a multiplexer output port, P row set portsand N transition input ports, wherein the multiplexer output port iselectrically coupled to the controller input port, the P row set portsare electrically coupled to the P select ports, and the N transitioninput ports are electrically coupled to the N transition circuits. 11.The keyboard device as claimed in claim 1, wherein if M key unitsKU(1,x)˜KU(M,x) in the x-th row are depressed in the scan cycle scan(k),the scan voltage is transmitted from the column signal line C(k) to thex-th row signal line R(x) through the key unit KU(k, x), and the un-scanvoltage is transmitted from the column signal lines C(1)˜C(k−1) andC(k+1)˜C(M) to the x-th row signal line R(x) through the other key unitsin the x-th row, wherein the scan voltage and the un-scan voltage aresimultaneously transmitted to the x-th row signal line R(x), and thetransition circuit TC(x) outputs the first voltage level even if voltageof the x-th row signal line R(x) is affected by both the scan voltageand the un-scan voltage.
 12. The keyboard device as claimed in claim 1,wherein the transition circuit TC(x) comprises: a voltage divider,electrically coupled to the x-th row signal line R(x), for generating avoltage at a comparison node according to voltage of the x-th row signalline R(x); and a switching circuit, electrically coupled to the voltagedivider, for selectively conducted according to the voltage at thecomparison node.
 13. The keyboard device as claimed in claim 12, whereinwhen the switching circuit is at an on state, the transition circuitTC(x) outputs the first voltage level; and when the switching circuit isat an off state, the transition circuit TC(x) outputs a second voltagelevel.
 14. The keyboard device as claimed in claim 12, wherein thetransition circuit TC(x) further comprises: a pull-up circuit,electrically coupled to the switching circuit and a high supply voltagesource.
 15. The keyboard device as claimed in claim 12, wherein thevoltage divider comprises: a first resistor, electrically coupled to thex-th row signal line R(x) and the comparison node; and a secondresistor, electrically coupled to the comparison node and a groundterminal, wherein the voltage divider generates the voltage at thecomparison node according to the first resistor and the second resistor.